It is known to filter out particles from dirty liquid by means of such a filter device, which is part of a self-cleaning filter installation. At certain intervals, the length of which depends primarily on the abundance of particles in the liquid, the particles which have adhered to the filter washers during the filtration are removed by back flushing of the filter rods. The back flushing occurs, after discharge of the dirty liquid, by compressed air being injected or by filtered clean liquid being pressed out of the core of the filter rods between the filter washers, so that the particles are detached from the outside of the filter rods and can be led away from the filter housing by discharging the liquid.
Such a filter installation is used, for example, in various types of machining operations, such as electrical discharge machining, grinding, polishing, honing and turning, in which particles are detached, to filter out these particles from the liquid that is used as cooling and/or lubricant liquid in the operation.
However, in some types of machining, in particular grinding, barbed particles form which tend to stick to each other and build up so-called socks round the filter rods. As these socks are permeable, they are unaffected by the back flushing and remain on the filter rods, which is a problem since the socks can thus continue to grow when continuing the filtration.
The filter rods are arranged in filter housings, which are closed containers integrated into the filter installation, and to take care of these socks the operator must thus stop the filtration, open the filter housings and lift up the filter rods, which results in a time-consuming stoppage. If the socks are not taken care of, they will finally grow so much as to destroy the filter rods or fill the housing with sludge, which entails a more serious stoppage that is more difficult to deal with.